1. Field of the Invention
The present invention relates to a controller for internal combustion engine to control an engine from cylinder to cylinder to bring an actual air-fuel ratio into a target air-fuel ratio.
2. Related Art
Conventionally, feedback control is performed to bring an air-fuel ratio of an air-fuel mixture to be taken in an engine into a target air-fuel ratio in order to prompt purification of exhaust gas from the engine. This manner of controlling an air-fuel ratio is realized for example by a method of controlling a fuel injection valve to regulate an amount of fuel contained in the air-fuel mixture, a method of controlling an air intake valve to regulate an amount of intake air, and other methods.
For instance, there is known an engine controller to control each cylinder into an optimum air-fuel ratio state (JP 2004-346807A). In this engine controller, an abnormal cylinder determination section determines an abnormal cylinder in which engine rotation variation occurs, based on a rotation angle signal from a rotation angle sensor. A rich/lean determination section determines whether or not an air-fuel ratio is shifted to a rich or lean side relative to a target air-fuel ratio based on an air-fuel ratio signal from an air-fuel ratio sensor. Based on abnormal cylinder information and rich/lean information, a shift level calculating section calculates a shift level of each cylinder. Furthermore, each cylinder injection valve correction amount calculating section calculates a correction amount with respect to a fuel injection amount of a fuel injection valve of each cylinder based on shift level information of each cylinder input from the shift level calculating section.
In such an engine system, part of exhaust gas discharged from an engine is returned to an intake system for the purpose of reducing exhaust emission, improving fuel consumption, and others. This recirculation of exhaust gas to the intake system is performed by an exhaust gas recirculation (EGR) system. To control EGR and others, generally, an EGR pipe is connected between an exhaust pipe and an intake pipe of an engine, and an EGR device (an EGR valve) provided at some midpoint in the EGR pipe to recirculate part of the exhaust gas to the intake system.